Accuracy of ambulatory blood pressure monitors in routine clinical practice

Background: To determine the extent of discrepancies between ambulatory blood pressure measurement (ABPM) devices and mercury sphygmomanometry in pre-use testing in routine clinical practice and whether such discrepancies are associated with patient characteristics and subsequent 24-h ABPM readings. Methods: A retrospective analysis of a database of 683 prospectively collected records was performed. The study population comprised of patients referred for ABP monitoring at a Sydney teaching hospital. Patients had same-arm sequential measurements with a mercury sphygmomanometer and Spacelabs 90207 or 90217 device before 24-h ABPM. The discrepancy between the test devices and the standard mercury sphygmomanometer were then described by two measures, calculated for both systolic and diastolic pressures for each patient: 1) difference of means (ABP average), and 2) the mean of differences between device measurement and the range of mercury sphygmomanometer readings, analogous to the British Hypertension Society protocol (ABP sequential). The main outcome measures were ABP average and ABP sequential and their relationship to patient characteristics. Results: The median ABP average was 1/2 mm Hg (ABPM device underestimation) and the median ABP sequential was 3/2 mm Hg. Age, gender, arm circumference, body mass index, and degree of hypertension influenced the accuracy of ABPM readings on multivariate analysis. Device accuracy was slightly weaker in patients with higher mercury or ABPM-derived systolic BP. Conclusions: These ABPM devices are accurate enough for routine clinical use in a variety of patients. Factors such as age, weight, gender, and severity of hypertension are statistically associated with greater device error but the differences are small enough to be unlikely to affect clinical practice.